37pfl7605h/12 power supply

[storexxm]

hello folks
i recently bought a broken 37pfl7605h/12 TV
the pre owner said it broke during watching tv. then he brought it to a technican and now i got it here. it seems like the fuse has taken out. guss there was some kind of shortcut? i couldn´t find any topics for this type of power supply (p973a)
maybe someone can tell me - what parts are the most common shortcuts... is it a good idea to just buy another fuse and set it on power ?
any suggestions are more then welcome =)

Just found this topic
https://www.circuitsonline.net/forum/view/134865
and i also have some burnt marks in this area.. guess this is the spot we are looking for ?!

[storexxm]

Re: 37pfl7605h/12 power supply

More details of the burnt area-

[dick_barton]

Re: 37pfl7605h/12 power supply

Has that blue capacitor burnt? If so that will need replacing. You would also need to check the two mosfets alongside.

[diif]

Re: 37pfl7605h/12 power supply

The fuse blew for a reason, don't just replace it. You've tested the components in the photo to see if any are shorted ? ?

[storexxm]

Re: 37pfl7605h/12 power supply

hello dick-
i bought this tv from someone else.. and he told my a technican already changed a component...
and this is the only area where obviosly something happened =)
so this SHOULD be a good capacitor... but for sure if i buy new parts i can change it.
but the real question is.. what caused a shortcut :/ i think its only one mosfet... and a diode. i am more a newbie.. so i measured only resistance in the circuit... no shortcut...
L603 has a very low resistance...

[storexxm]

Re: 37pfl7605h/12 power supply

@ diif just q602 d602 (high)
and L603 (low)

[dick_barton]

Re: 37pfl7605h/12 power supply

Use you meter set to ohms and with the set discoonected from the mains supply check the 4 legs of the bridge rectifier.
bridge rectifier legs 1 - 2 -3 - 4

Test
leg1 to 2, then to 3, then to 4
leg 2 to 3 then to 4
leg 3 to leg 4

and what readings do you have in ohms

[storexxm]

Re: 37pfl7605h/12 power supply

1-2 98,5k then 130k
1-3 109,5k then 115k
1-4 15,05k then 15k

2-3 2,11M
2-4 96k then 135k

3-4 146k

but its changing.. !?
are those values useful ? i measured the bridge on the board.. didnt solder it out-

[dick_barton]

Re: 37pfl7605h/12 power supply

The bridge rectifier looks OK with no short circuit. Sometimes when there is a major short circuit it can damage the bridge rectifier.
I would check the mosfets for short circuit and also test as many of the diodes as you can with the meter set to diode mode.

[budm]

Re: 37pfl7605h/12 power supply

Can we see good clear straight shots of the whole bottom side of the power supply board?

[storexxm]

Re: 37pfl7605h/12 power supply

For sure!

[dick_barton]

Re: 37pfl7605h/12 power supply

What were the results when you checked those two mosfets on the heatsink alongside the blue capacitor.
What is written on that capacitor?

[storexxm]

Re: 37pfl7605h/12 power supply

The blue one says:
471k
1kv
Measured 15k-20k ohm

Mosfet Q602

1-2 28k
2-3 14k
1-3 9,5k

Diode D602

9,1k

L603

0,3 Ohm

D601

96k or 1,00M depends on + -

R613

0,3 Ohm

TH601

3,3 Ohm

[dick_barton]

Re: 37pfl7605h/12 power supply

Those readings don't show a short circuit. There's a second bridge rectifier on the board which you can test as you did earlier.
Without a schematic it's hard to pin down any fault.

[storexxm]

Re: 37pfl7605h/12 power supply

I measured it already... no shortcut.. but can post values tomorrow.
What can happen when I short the missing fuse and look what happens... guess the right fuse will just blow away and I know as much as before... ^^

[budm]

Re: 37pfl7605h/12 power supply

1) Looking at the solder joints of the Blue Snubber cap for the PFC MOSFET, it does not looks like it was replaced, I do not see any flux residue at all, but then the pictures may not be showing it.

2) There is burnt solder joints in the transformer legs, you need to clean it up and re-solder them well. It looks like it has been arcing for quite a while.

3) Check those two MOSFET's to make sure they are not shorted.

4) You should also check all other solder joints real well too.

[storexxm]

Re: 37pfl7605h/12 power supply

Hello budm. Honestly when i looked at the board closer i had the same thought... looks like this condenser is original... but where are those burnt marks at the surface? From the yellow coil? Will check the two mosfets for a short. Didn't measure on the bottom side yet (shame)
Thanks for your tips!!!

[budm]

Re: 37pfl7605h/12 power supply

Hello budm. Honestly when i looked at the board closer i had the same thought... looks like this condenser is original... but where are those burnt marks at the surface? From the yellow coil? Will check the two mosfets for a short. Didn't measure on the bottom side yet (shame)
Thanks for your tips!!!

Make sure to look real close at those solder joints I marked in the picture.

[storexxm]

Re: 37pfl7605h/12 power supply

i will check them asap when home.
Thank you !

[storexxm]

Re: 37pfl7605h/12 power supply

Ooops. Those solder joints u marked... BD401
The two middle legs are a short !
Thank u budm! Can this be the issue ?
Part No. says: D4SBL20U and smaller letters 6304 afterwards.
Is the D4SBL20U enough to look for a new one?